The present invention relates to a method and apparatus for retrieving a running tool/guideframe assembly from the ocean floor following riser installation without the need for winch wires.
In conventional offshore drilling techniques, a running tool/guideframe assembly is used to connect the production riser to the subsea wellhead. The running tool/guideframe assembly is attached to the leading end of the riser and is guided into position above the wellhead by lowering the running tool/guideframe assembly down previously installed guidelines that are attached to guideposts on the well template.
Winch wires are used in the conventional method to control the lowering of the assembly and then to retrieve the same following connection of the riser to the wellhead. The use of winch wires invariably leads to problems. A minimum of two winch wires are needed to maintain the running tool/guideframe assembly substantially horizontal to avoid binding on the guidelines. However, it is virtually impossible to let out two wires simultaneously at the identical rate. Hence, one or the other of the wires will wind up with slack in it which will invariably take a wrap around something it ought not be wrapped around. When this occurs, the lowering must be suspended and a diver or remotely operated vehicle sent down to try to untangle the winch wire. When drilling an offshore well, time is money, more money than almost anywhere else. When time has to be needlessly wasted in unproductive operations such as untangling winch wires, it tends to increase the frustration level of all concerned. The difficulty is exacerbated in deep water because of the additional cable lengths necessary.
The present invention is directed to a method and apparatus designed to overcome these problems by eliminating the need for winch wires. The guidepost system on the well template is modified so that a portion thereof may be unlatched. Further, the unlatched portion is provided with a load supporting means that can engage and lift the running tool/guideframe assembly. In this manner, the riser itself may be utilized to lower the running tool/guideframe assembly along the guidelines and then the assembly may be retrieved following unlatching of a portion of each of the guidepost assemblies and disconnection of the running tool from the riser by reeling in the guidelines.
Various other features, advantages and characteristics will become apparent after a reading of the following detailed description.